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A small tree, occasionally up to 30 ft high, with a trunk 1 to 11⁄2 ft in girth, but, according to Sargent, more often a shrub; young shoots at first downy, becoming glabrous later. Leaves obovate, sometimes oval or ovate, 2 to 4 in. long, 11⁄4 to 21⁄2 in. wide; wedge-shaped at the base, with short, broad points, the margins set with small, gland-tipped teeth; upper surface dark glossy green, glabrous; lower one dull, glabrous or with tufts of down in the vein-axils; stalks slightly downy, 1⁄2 to 3⁄4 in. long. Male flowers yellow, expanding in autumn on rough-stalked pendulous catkins 11⁄2 to 21⁄2 in. long, formed the same summer in the uppermost leaf-axils. Female catkins about 1⁄6 in. long at the time of fertilisation, expanding and ripening the following year into egg-shaped fruits 5⁄8 to 3⁄4 in. long.
Native of Delaware and Maryland; usually found near water. It was raised from seed sent by Prof. Sargent to Kew in 1878, and a tree by the lake side succeeded well until 1895, when it succumbed – apparently to the great frosts of February of that year, the effect of which, no doubt, had been heightened by the low, wet situation in which it grew. Reintroduced in 1899, but not grown at Kew at the present time. Its habit of flowering in autumn distinguishes this species from all other cultivated alders except A. nepalensis and A. nitida.
This species is again in cultivation at Kew, where there are four examples by the near end of the Lake.
A. maritima is evidently a relict species. Even in Delaware and Maryland it is confined to a small area; it has a widely disjunct second area in southern central Oklahoma (Furlow).